The present invention is particularly useful for constructing leaching chambers made of molded thermoplastic, which chambers are buried underground for use, and which chambers have been in widespread use with small domestic and industrial wastewater treatment systems for a number of years. See U.S. Pat. No. 4,759,661 of Nichols et al. Such type chambers may also be used for draining earth or other media.
Leaching chambers used heretofore have various kinds of sidewall perforations, to enable waters received in the chamber to percolate into the soil. Some prior art chambers have plain round holes and are overlaid with geotextile (water permeable woven or non-woven fabric, also called filter fabric) to prevent the infiltration of soil into the chamber interior. The present invention improves upon arch shape cross section molded chambers of the prior art which have downward sloping slots in the sidewalls, which chambers are intended to be functional without the use of geotextile. The conventional approach in the art has been to shape the slots and chamber sidewalls so that the slot bottoms are downwardly sloped, and so that the slot depth is sufficient to inhibit soil entry into the chamber interior. The prevalent approach has been to provide louvers above and below the opening of each slot. The effect of that is to increase the thickness of the sidewall of the chamber and thus the slot depth, compared to the thickness of the wall where there are no slots, and often, compared to regions laterally adjacent to the slots. For example, the sidewall thickness at louvers may be around 0.5 inch, when the wall elsewhere is about 0.130 inch. However, the approach increases chamber weight and cost.
A typical prior art slot has a downward sloping bottom surface and a horizontal or downward sloping upper surface. Typically, prior art injection molded plastic chambers are made in a two part mold, comprised of a core male part and a cavity female part; and the slides move in and out within the cavity part, to create the slots. The slots in prior art injection molded chambers are made by having slides, i.e., movable mold parts, which penetrate into the space in the mold which defines the chamber article, from the outer or cavity portion of the mold, i.e., that which forms the exterior surface of the chamber. The slides that define the slots typically have a draft, typically 3 degrees or more, for convenience of withdrawal of the slide from the molded part. Thus, the resultant slot will have outward flare, even if intended to be straight. Some prior art designs slope the bottom surface of the slot more than the top, so the outward flare will be greater than draft considerations dictate.
Now, it is desirable to improve upon the prior art technology, and to make chambers having sidewalls which are lighter than heretofore, and which have shorter length slots or other perforations.